Ion-assisted collection of Nylon-4,6 electrospun nanofibers

In electrospinning, electrostatic interaction between charged fibers and the collection substrate can result in poor and non-uniform coverage, particularly when electrically insulating substrates are used, because they are prone to surface charge accumulation. Charged electrospun Nylon-4,6 nanofiber coatings were deposited onto substrates of varying size, conductivity and morphology. The density and uniformity of the nanofiber coatings were significantly enhanced, both on insulating and on conducting substrates, by a new method based on rapid sequential deposition of charged nanofibers and oppositely charged ions onto substrates that were mounted onto a rotating collecting electrode (mandrel) located between an electrospinning source and a focused ion source. Sequential fiber/ion deposition presumably led to surface charge neutralization or reversed charging, and minimization of electrostatic fiber/substrate interactions. An electrostatics model was developed to interpret the experimental results. It was also theoretically argued that any degree of ion charging will induce continuous fiber accumulation.     

Charge consequences in electrospun polyacrylonitrile (PAN) nanofibers

During the last 10 years extensive research has been conducted on various aspects of electrospinning. These efforts include spinning many different polymer and solvent pairs, varying fiber forming conditions, fiber characterization and process modeling. In this work we explore some issues related to charging of the polymer solution, namely charge quantification of electrospun fibers and different charge delivery designs. PAN fibers electrospun in our laboratory show a charge density of 30-50 nC/mg. The charge density varied with applied voltage and solution properties. Theoretical charge density calculations agree well with experimental measurements. Different charging approaches, such as positive or negative induction charging and ionized field charging, all led to fine fiber formation.     

Rechargeable thin film batteries of polypyrrole and polyaniline

Thin films of polypyrrole (PPy) and polyaniline (PANi) were electrochemically deposited on stainless steel substrate under potentiostatic control. Secondary batteries were assembled using these polymers as active electrode materials and propylene carbonate (PC) solutions of tetraethyl ammonium perchlorate (TEAP) as the electrolyte. In repeated charge and discharge tests, the all PANi cells performed better than the PPy-PANi cells in voltage characteristics, recyclability, charge retention and coulombic efficiency. There appears to be an optimum charging current for the polymer cells and charging the cells at rates notably different from the optimum value reduced the cell performance substantially. It is suggested that the cells operate under kinetic control and charging at extreme rates either reduces the participation of polymer redox in the overall cell operation or produces mass transfer limitations.     

Electrospun ultrathin nylon fibers for protective applications

Electrospun nylon 6 fiber mats were deposited on woven 50/50 nylon/cotton fabric with the motive of making them into protective material against submicron‐level aerosol chemical and biological threats. Polymer solution concentration, electrospinning voltage, and deposition areal densities were varied to establish the relationships of processing‐structure‐filtration efficiency of electrospun fiber mats. A high barrier efficiency of greater than 99.5% was achieved on electrospun fiber mats without sacrificing air permeability and pressure drop. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Open circuit voltage recovery of discharged and shorted nickel-cadmium cells

The open circuit voltage recovery transient of a positive-limited nickel-cadmium cell has been theoretically analysed taking into account the double-layer charging process, polarization due to charge transfer, mass transfer and ohmic resistance in the cell, and self-discharge due to any internal electronic short. Expressions have been obtained for charge transfer and mass transfer polarization. Experimental data on open circuit voltage recovery transients obtained for nickel-cadmium cells indicate that the rate of the electrode reaction at the positive electrode of the cells is controlled by mass transfer process.     

Fabrication of nanofibers by a modified air-jet electrospinning method

A modified air-jet electrospinning (MAE) setup was demonstrated for contributing to the large-scale nanofibers production. With this single nozzle air-jet electrospinning device, the productivity of nanofibers can be increased more than forty times as compared with using the single-needle electrospinning (SNE) setup. When compared with other needle-less electrospinning setups, the benefits of this setup include ability to keep stable concentration of electrospun solution and to produce more uniform and thinner fibers, controlling of the jets formed speed and position, higher throughput, lower critical voltage, easier assembling, simpler operation, and so on. Four different parts of the fiber generator were, respectively, charged as electrospun electrodes to produce fibers. The distributions of the electric field with different electrodes were simulated and investigated for explaining the experimental results including the fibers productivity, the deposition area of nanofiber mats, as well as the surface morphology of the fibers. When the whole nozzle was charged, as compared with charging other electrodes, the MAE system produced thinner fibers with larger standard deviation on a much larger scale. By reduction of charged area, the received fibers presented lower productivity and thicker diameter with lower standard deviation. Especially, when a half of the nozzle was charged, the deposition area of nanofiber mats was larger than charging other electrodes. Besides, when a half of the nozzle was charged, the influences of electrospinning parameters such as applied voltage, collecting distance and the flow rate of air on nanofibers morphology were also investigated. Furthermore, based on this spinning unit, multi-nozzle air-jet electrospinning setup can be designed for larger production of nanofibers.     

An investigation into the influence of electrospinning parameters on the diameter and alignment of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibers

Electrospinning is an effective technology for the fabrication of ultrafine fibers, which can be the basic component of a tissue engineering scaffold. In tissue engineering, because cells seeded on fibrous scaffolds with varying fiber diameters and morphologies exhibit different responses, it is critical to control these characteristics of electrospun fibers. The diameter and morphology of electrospun fibers can be influenced by many processing parameters (e.g., electrospinning voltage, needle inner diameter, solution feeding rate, rotational speed of the fiber‐collecting cylinder, and working distance) and solution properties (polymer solution concentration and conductivity). In this study, a factorial design approach was used to systematically investigate the degree of influence of each of these parameters on fiber diameter, degree of fiber alignment, and their possible synergetic effects, using a natural biodegradable polymer, poly(hydroxybutyrate‐co‐hydroxyvalerate), for the electrospinning experiments. It was found that the solution concentration invoked the highest main effect on fiber diameter, whereas both rotational speed of the fiber‐collecting cylinder and addition of a conductivity‐enhancing salt could significantly affect the degree of fiber alignment. By carefully controlling the electrospinning parameters and solution properties, fibrous scaffolds of desired characteristics could be made to meet the requirements of different tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The mechanism of the controlled deposition of electrospun fibers

The controlled deposition of electrospun fibers means that the electrospun fibers can be collected in a limited and specified area and can present better applications in the fields of medical treatment, garment making, and 3D printing. In order to study the mechanism of the controlled deposition of electrospun fibers, simulation and experimental methods were used. Specifically, in the electrospinning experiment, circular copper sheets of different diameters were used as collectors. The effect of different collector areas on the morphology of fiber deposition was discussed. The electric field distribution of electrospinning with different specifications of collectors was simulated correspondingly. The experimental results show that, as compared to the traditional large flat collector, the area where the electrospun fibers are deposited is significantly reduced when a smaller circular copper plate was used as a collector. The smaller the area of the collector, the more the fibers tend to deposit at the center area of the collector, and the more likely the morphology of the product formed by the fiber deposition to exhibit a center protrusion shape. The controlled deposition of the electrospun fiber technology can provide more opportunities for the application of the electrospinning technology.     

电晕放电喷雾荷电特性

静电喷雾广泛应用于工业各个领域,如静电喷涂、静电雾化燃烧、静电雾化除尘等,其应用效果与喷雾荷电特性密切相关。为获得更佳荷电效果,本文探究了电晕荷电过程中感应电流对液滴真实荷电电流的影响,通过改变荷电电压、电极间距、电极环直径及液体流量等,实验研究了各因素变化对喷雾荷质比、电荷衰减及液滴粒径的影响。结果表明：相比于感应荷电,电晕荷电过程不稳定但能获得更佳的荷电效果,液滴荷质比随荷电电压的增加而先减小后增大,随电极环直径的增加而先增大后减小,随电极间距的增大而增大,电极环直径80mm,电极间距40mm能获得最佳荷电效果;荷电液滴带电量会随输运距离增加而泄漏衰减,相同距离下液滴通过电晕放电带有电荷后衰减更快;液滴带电后能够降低液体表面张力,随着液滴荷电量的增加,雾化液滴粒径有所降低。     

A dynamic liquid support system for continuous electrospun yarn fabrication

Electrospinning is known to be a highly versatile process which is able to produce fibers made out of different compositions with diameter of a few microns down to several nanometers. Current electrospinning technology generally involves the deposition of fibers onto a solid substrate although in some cases, a liquid coagulation bath is used to collect the fibers. However, a liquid collector may offer several advantages over a solid substrate. A novel electrospun fiber manipulation process through the use of a water vortex is described in this communication where continuous yarn was made from electrospun fibers. Preliminary studies on some parameters such as solution feed rate and solution concentration and their impact on fabrication of the yarn and the fiber morphology were carried out.     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Alignment and optimization of nylon 6 nanofibers by electrospinning

Nonwoven electrospun nylon 6 nanofibers produced with formic acid under different concentrations have been examined. The effects of the solution properties, electric field, and spinneret‐to‐collection distance on the fiber uniformity, morphology, and average diameter have been established. The optimum polymer solution concentration (20 wt %), applied voltage (15 kV), and spinning distance (8 cm) have been found to make uniform nylon 6 fibers. A simple technique that can produce a bundle of aligned electrospun fibers suspended between two grounded disks is described. Alignment and stretching of the fibers are derived by the electrostatic interactions between the positive electrode on the spinneret and the grounded disks. The gap between the disks and the collection time have been varied to systematically study the degree of alignment and the density of the collected nylon 6 fibers. The number of the distributed fibers in the bundle can be controlled by the alteration of the deposition time, the voltage, and the width of the gap. Scanning electron microscopy images have indicated a greater degree of fiber alignment with increasing disk gaps and collection times. The article also provides a comprehensive review of the design of various mechanisms for nanofiber alignment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Cyclic voltammetric study of the corrosion protection of metal surfaces by plasma-polymerized coatings

The corrosion-protective performance of plasma-polymerized (PP) films on metal substrates has been investigated by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and surface potential measurements. A PP film from cyclohexane was deposited on Fe, Ni, and Cu substrates using a radiofrequency generator. A PP film-coated metal substrate was employed as the working electrode in aerated NaCl aqueous solution and the cyclic voltammogram was measured repeatedly ten times upon application of a triangular potential between -1 and 1 V vs. the initial corrosion potential of the sample. The cyclic voltammogram depended strongly on the metal substrate: with Fe and Ni, only an anodic current was observed; with Cu, an anodic and subsequently a cathodic current appeared. For all the metals, the anodic current level in the voltammograms at the same potential sweep number decreased with increasing film deposition time. The anodic current level for Fe and Cu increased with increasing potential sweep number, but that for Ni exhibited a maximum, followed by a decrease. The anodic current level for the metal substrates decreased in the order Fe > Ni > Cu. The cathodic current for Cu decreased with an increase in the deposition time and increased with an increase in the potential sweep number. The dependence of the cyclic voltammogram on the metal substrate is discussed in terms of the PP film thickness and the positive charge on the film surface, as well as the standard reduction potential of the metal. The corrosion potential for PP film-coated metal substrates also changed with the deposition time; this change is suggested to be related to the increase in the positive charge on the surfaces.     

可溶铅酸液流电池模拟与仿真

可溶铅酸液流电池是一种使用单个容器存储电解液并且不需要微孔隔膜的氧化还原液流电池,这使得电池设计简单并降低了成本。建立二维暂态可溶铅酸液流电池模型,模型基于对质量、电荷以及能量的转移与守恒以及包含铅离子反应的宏观动力学模型为基础,研究了电极间隔、电极形状、电流密度、实验温度、入口电解液流速和电解质初始浓度对电池性能的影响。研究表明：与平板电极相比,弧形电极明显提高了充电时的电池电压。在影响铅酸液流电池性能的诸多条件中,电池温度和电流密度可能是优化电池性能的重要因素。     

Charging/discharging kinetics of poly(3,4-ethylenedioxythiophene) in 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ionic liquid under galvanostatic conditions

The constant current charging/discharging experiments of poly(3,4-ethylenedioxythiophene) (PEDOT), modified electrodes in room temperature ionic liquid, for instance 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide, were performed for two types of cell configurations, three and two-electrode cells. In each case, a linear variation of the voltage with respect to time was observed. The electrochemical responses were analyzed in term of a series combination of a resistance R and a capacitor C. Accordingly, the capacitance of the modified electrodes was determined. One observed a linear variation of the capacitance as a function of the amount of PEDOT. This capacitance described the chemical capacitance of PEDOT that reflected the capability of the system to accept or release additional charge carriers on a given variation of the chemical potential. Also, the electrochemical response during constant current charging/discharging experiments for two-electrode cell in which the same amount of PEDOT was deposited on each electrode showed a type I electrochemical supercapacitor response. This kind of an electrochemical chain allowed us to mimic and to analyze the electrical responses of an electrochemical actuator based on an interpenetrating polymer networks containing PEDOT that was able to work in air.     

静电纺PCL纤维形态与热性能的研究

利用静电纺丝法制备了超细聚ε-己内酯(PCL)纤维;借助扫描电镜仪和差示扫描量热仪表征了PCL纤维的形态与热性能;研究了电纺过程中溶液浓度、电压、接收距离和纺丝速度对纤维形态的影响。结果表明:当纺丝电压为10 kV,接收距离为15 cm,纺丝速度为2 mL/min时,纺丝液中PCL质量分数为6%~12%能获得连续无串珠的纤维;纺丝电压为8~12 kV,电纺过程稳定;接收距离对纤维的直径和形貌无明显影响;与流延成型的PCL膜相比,电纺PCL纤维具有较低的结晶度。     

Electrospinning of thermoplastic polyurethane microfibers and nanofibers from polymer solution and melt

Electrospinning technique was used to produce ultrafine fibers from thermoplastic polyurethane (TPU). A direct comparison between melt and solution electrospinning of TPU was provided for the evaluation of process–structure relationship. It was found that the deposition rate of melt electrospinning (0.6 g h^?1) is four times higher than that of solution electrospinning (0.125 g h^?1) for TPU under the same processing condition. However, the average fiber diameters of solution electrospun TPUs (220–280 nm) were much lower than those of melt electrospun TPUs (4–8 μm). The effect of processing variables including collection distance and electric field strength on the electrospun fiber diameter and morphology was also studied. The findings indicate that increasing the electric field strength yielded more electrical forces acting on polymer jet and resulted in a decrease in fiber diameter as a result of more fiber drawing in both solution and melt electrospun fibers. It was also demonstrated that increasing the collection distance led to an improvement in the solidification of melt electrospun fibers and thus less fused fibers were obtained. Finally, a close investigation of fiber structures revealed that melt electrospun TPU fibers had smooth surface, whereas solution electrospun TPU fibers showed high intensity of cracks on the fiber surface. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization of deposition patterns produced by twin-nozzle electrospray

This paper presents the characteristics of two-nozzle electrospray deposition with a capillary–extractor–substrate configuration. A three-dimensional Lagrangian model was developed to simulate the spray evolution and deposition patterns. The droplet size distribution was not affected by the extractor–substrate voltage; however, spray evolution was found to be influenced considerably by the extractor–substrate voltage. Smaller particles are deposited densely in the outer region of the spray, whereas larger particles are deposited in the core region of the spray due to the size segregation effect. The normalized thickness in the intervening region of adjacent sprays is thinner than in the core region of sprays and gradually decreases as the extractor–substrate voltage increases. The normalized surface number density of deposited particles in the intervening region of adjacent sprays also decreased with the increasing extractor–substrate voltage, whereas the surface number density of them is larger than that in the core regions of sprays at an extractor–substrate voltage below 3 kV. The deposition patterns using a diluted PSL solution and spray visualization were in good agreement with the simulation results. It is suggested that the electrical self-dispersion effect and electrical repulsive interaction between adjacent sprays play an important role in determining the characteristics of the spray evolution and deposition patterns for multiplexed electrospray deposition.     

Optimization of the electrospinning conditions for preparation of nanofibers from polyvinylacetate (PVAc) in ethanol solvent

In order to fabricate polyvinylacetate (PVAc) fiber by electrospinning, we have been examined electrospun polyvinylacetate (PVAc) under various conditions after dissolving it in ethanol solution. As the concentration of spinning solution increased, the diameter of the electrospun PVAc fiber increased. At the concentration lower than 10 wt.%, beads were formed while over the 25 wt.%, distinct fiber was not observed. At the tip-collector distance (TCD) of 7.5 cm or less, the jet of spinning solution was unstable and the fiber diameter decreased. On the other hand, at the TCD of 10 cm or more, the strength of electric field became too weak and the fiber diameter increased. As the flow rate of spinning solution increased, the fiber diameter increased and at the flow rate of 300 μl/min or more, it increased sharply. For 15 wt.% PVAc, the fiber diameter decreased as the applied voltage increased. At a high-applied voltage, however, charge acceleration caused the spinning solution not to be separated and thus the fiber diameter increased. As a result of dissolving PVAc in ethanol and electrospinning it in the following conditions, a fiber with the diameter of about 700 nm was spun: the concentration of 15 wt.%, the TCD of 10 cm, the spinning solution flow rate of 100 μl/min, and the applied voltage of 15 kV.     

Charge transport mechanisms and memory effects in amorphous TaNx thin films

Amorphous semiconducting materials have unique electrical properties that may be beneficial in nanoelectronics, such as low leakage current, charge memory effects, and hysteresis functionality. However, electrical characteristics between different or neighboring regions in the same amorphous nanostructure may differ greatly. In this work, the bulk and surface local charge carrier transport properties of a-TaN_x amorphous thin films deposited in two different substrates are investigated by conductive atomic force microscopy. The nitride films are grown either on Au (100) or Si [100] substrates by pulsed laser deposition at 157 nm in nitrogen environment. For the a-TaN_x films deposited on Au, it is found that they display a negligible leakage current until a high bias voltage is reached. On the contrary, a much lower threshold voltage for the leakage current and a lower total resistance is observed for the a-TaN_x film deposited on the Si substrate. Furthermore, I-V characteristics of the a-TaN_x film deposited on Au show significant hysteresis effects for both polarities of bias voltage, while for the film deposited on Si hysteresis, effects appear only for positive bias voltage, suggesting that with the usage of the appropriate substrate, the a-TaN_x nanodomains may have potential use as charge memory devices.